WO2005086391A1 - Systeme, procede et dispositif de compensation de dispersion de polarisation de mode et de demultiplexage de signaux multiplexes de polarisation - Google Patents

Systeme, procede et dispositif de compensation de dispersion de polarisation de mode et de demultiplexage de signaux multiplexes de polarisation Download PDF

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Publication number
WO2005086391A1
WO2005086391A1 PCT/EP2005/051061 EP2005051061W WO2005086391A1 WO 2005086391 A1 WO2005086391 A1 WO 2005086391A1 EP 2005051061 W EP2005051061 W EP 2005051061W WO 2005086391 A1 WO2005086391 A1 WO 2005086391A1
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WIPO (PCT)
Prior art keywords
accordance
polarization
signals
fibre
transfer matrix
Prior art date
Application number
PCT/EP2005/051061
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English (en)
Inventor
Marco Secondini
Enrico Forestieri
Giancarlo Prati
Giulio Colavolpe
Original Assignee
Ericsson Ab
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Publication date
Application filed by Ericsson Ab filed Critical Ericsson Ab
Priority to US10/598,718 priority Critical patent/US7873282B2/en
Priority to EP05716976A priority patent/EP1723737A1/fr
Priority to JP2007502345A priority patent/JP2007528175A/ja
Publication of WO2005086391A1 publication Critical patent/WO2005086391A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2569—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to polarisation mode dispersion [PMD]

Definitions

  • the present invention relates to the field of demodulation techniques for optical communication systems and in particular although not exclusively to demodulation of polarization multiplexed signals.
  • polarization multiplexing allows the transmission at the same carrier wavelength in the same optical fibre of two orthogonally polarized optical signals, thus doubling the spectral efficiency. In this manner it is possible to double the amount of data transmitted in a unit of time whilst occupying the same wavelength band.
  • Wavelength Division Multiplexing With reference to a Wavelength Division Multiplexing (WDM) system, the use of PolMUX can be viewed from two perspectives: the first being a 4-level transmission system allowing a doubling of the transmission rate per wavelength channel without changing the transmitted symbol speed (for example a 40Gbi1/s channel can be transmitted in the form of two 20Gbit/s orthogonally polarized optical signals), and the second a method of doubling the number of WDM channels without changing (reducing) the wavelength channel spacing.
  • WDM Wavelength Division Multiplexing
  • PolMUX presents considerable practical difficulties in implementing it in optical communications system.
  • an optical signal which is transmitted over an optical fibres undergoes random time- varying rotation to its state of polarization.
  • the state of polarization of the received optical signal is subject to random time-varying rotation.
  • this phenomenon will not affect the orthogonality of the two polarization multiplexed signals it will affect the orientation with the orthogonal states of polarization are presented to the receiver thus making their separation impossible without an appropriate dynamic polarization tracking technique.
  • PMD Polarization Mode Dispersion
  • the present invention arose in an endeavour to at least in part remedy the above mentioned shortcomings and provides a system that allows simultaneous PMD compensation and demultiplexing of polarization multiplexed signals.
  • a transmission system comprising two optical signals transmitted over the same fibre at the same wavelength but with orthogonal polarization and characterised by receiving apparatus capable of filtering the two components with orthogonal polarization of the signal received in accordance with a transfer matrix which is controlled dynamically on the basis of the output signals in such a manner as to approximate the reverse transfer matrix of the fibre in the region of the spectrum occupied by the signal so as to compensate for the PMD and the polarization rotation introduced by the fibre and elin inating distortion and mutual interference effects for both the signals and obtaining at output an approximate repetition of the two signals transmitted.
  • a transmission method comprising two optical signals transmitted over the same fibre at the same wavelength but with orthogonal polarization and characterised by at the receiving side filtering the two components with orthogonal polarization of the signal received according to a transfer matrix and dynamically controlling the transfer matrix on the basis of the signals output in such a manner as to approximate the reverse transfer matrix of the fibre in the region of the spectrum occupied by the signal so as to compensate for the PMD and the polarization rotation introduced by the fibre while eliminating distortion and mutual interference effects for both the signals and obtaining at output an approximate repetition of the two signals transmitted.
  • PMD polarization mode dispersion
  • FIG. 1 is a block diagram of a polarization multiplexing transmission system in accordance with the invention.
  • FIG. 2 is a functional block diagram of the demultiplexing DMUX apparatus of Figure 1 as a combination of transversal filters with complex coefficients;
  • FIG 3 is a practical implementation of the DMUX apparatus of Figure 2 implemented w in the form of a Planar Lightguide Circuit (PLC);
  • PLC Planar Lightguide Circuit
  • Figure 4 shows another possible implementation of the DMUX of Figure 2 using Polarization Controllers (PC) and Polarization Ma taining Fibres (PMF);
  • PC Polarization Controllers
  • PMF Polarization Ma taining Fibres
  • FIG. 5 is a block diagram of the transfer functions to which the signals are subjected in the system of Figure 1;
  • Figure 6 are two channel eye diagrams before (left hand side) and after (right hand side) filtering by the planar lightguide circuit (PLC); and Figure 7 plots of outage probability versus normalised mean differential group delay (DGD) for the polarisation multiplexing system of the invention compared to an uncompensated on off keying (OOK) and first order compensated OOK systems.
  • PLC planar lightguide circuit
  • two independent bit streams «; and a 2 are applied to two respective transmitters TX 13 which produce corresponding intensity modulated optical signals zi and z 2 with the same carrier wavelength ⁇ .
  • the transmitter 13 conveniently comprises a single laser for generating the optical carrier, an optical splitter for splitting the laser light and a respective optical modulator for modulating light from the laser with the bit streams ⁇ ; and o 2 .
  • the two modulated optical signals z. and z 2 of carrier wavelength ⁇ are combined such that their respective states of polarization are orthoganol to one another by a Polarization Beam Combiner (PBC) 14 and the polarization multiplexed signal transmitted through an optical fibre 15 to the receiving stage 11.
  • PBC Polarization Beam Combiner
  • the received polarization multiplexed signal is separated into two orthogonal components by a Polarization Beam Splitter (PBS) 16 whose axes are arbitrarily oriented.
  • PBS Polarization Beam Splitter
  • the two separated components xi and x 2 are applied to a respective input port of a demultiplexing (DMUX) device 17 to produce components yi and y at respective output ports of the device.
  • DMUX device 17 will be described in detail below and can be fabricated in the form of a Planar Lightguide Circuit (PLC) or as a cascade of discrete components such a Polarization Controllers and Polarization Ma t ⁇ ining Fibres.
  • PLC Planar Lightguide Circuit
  • the two output components yi and y 2 correspond to the two transmitted signals z? and z 2 appropriately equalized and demultiplexed to compensate for the effects of the propagation through the fibre 15.
  • the components yi and y are detected by a respective photodetector 18 to produce corresponding electrical signals si and s 2 which are input to known receiver (RX) 19.
  • the receivers 19 produce respective output signals ⁇ i and ⁇ 2 which by appropriate configuration and control of the DMUX "will correspond to the original bit stream signals a 7 and a 2 .
  • the receivers 19 for the two channels can be completely separate or share some elements such as the clock recovery circuit.
  • the DMUX device 17 is advantageously adaptively controlled by continually updating the value of its control parameters on the basis of a feedback signal derived from the signals j, s 2j & ⁇ and ⁇ .
  • a control circuit 20 controls the DMIUX device control parameters on the basis of a feedback signal which is generated by a block 21 which calculates said signal on the basis of the characteristics of the signals j, s 2 , & ⁇ and ⁇ 2 .
  • FIG. 2 shows a functional diagram of the demultiplexing DMUX device 17 by means of a combination of a plurality N of transverse filters with complex coefficients that are indicated below as two-dimensional filters.
  • the DMUX device has transfer function H( ⁇ ) given by:
  • FIG 3 shows a schematic representation of a possible implementation of the DMUX device 17 that is implemented as a Planar Lightguide Circuit (PLC).
  • the device 17 is a 4-port device, two input and two output ports, and comprises a cascade of N identical filtering elements.
  • variable coupler 23 controlled by a parameter ⁇ n for coupling optical
  • DMUX device will be readily imaginable to one skilled in the art, and can comprise for example a Mach-Zehnder interferometer type structure.
  • some, or all, of the N elements of the device include a larger number of phase modulators 22 and variable couplers 23 to increase the number of degrees of freedom of the device.
  • the overall transfer matrix of the device can be calculated by multiplying the transfer matrices of the individual elements. In particular, by omitting an unessential delay phase term, the transfer matrix of the variable coupler H ⁇ , phase modulator H ⁇
  • the transfer matrix (6) is a frequency-dependent unitary transfer matrix that can be written in the same form indicated by equations (1) to (4). Accordingly, the PLC (Planar Lightguide Circuit of Figure 3) device realizes the functionality requested of the DMUX 17 device. In practice, it is necessary to allow for the fact that the control parameters will not be directly the complex coefficients of the transverse filter but the Q parameters of the PLC linked thereto non-linearly. This does not present a problem for realization of the present invention.
  • Figure 4 illustrates an alternative implementation of the DMUX 17 using cascaded polarization controllers (PC) and polarization maintaining fibres (PMF).
  • PC cascaded polarization controllers
  • PMF polarization maintaining fibres
  • the operating principle of the DMUX 17 apparatus is based on the controllability of its transfer matrix.
  • the device In the event of choosing a value of ⁇ sufficiently small (for example half of the bit period of the input signal) and having a sufficiently large number N of stages (4 stages, for example) the device is capable of approximating the reverse transfer matrix of the fibre in the region of the spectrum occupied by the signal.
  • the two output signals are essentially an (approximate) reproduction of the signals transmitted.
  • U( ⁇ ) represents the Jones matrix of the optical fibre 15 and allows for the rotation effects and Polarization Mode Dispersion (PMD) with a reference system which at input is aligned with the axes of the Polarization Beam Combiner (PBC) and at the output to those of the Polarization Beam Splitter (PBS).
  • PMD Polarization Mode Dispersion
  • FIG. 6 An example of operation of the DMUX device 17 is shown in Figure 6, which shows two channel eye- diagrams before (left hand side) and after (right hand side) filtering by the DMUX device 17.
  • the DMUX device is fabricated in form of a planar lightwave circuit (PLC) and the eye diagrams are for PolMUX transmission over a fibre affected by Polarization Mode Dispersion (PMD).
  • PLC planar lightwave circuit
  • PMD Polarization Mode Dispersion
  • the eye diagrams for both channels are shown at for the input and output of the DMUX. From a comparison of the eye diagrams it is evident that the distortion and mutual interference caused by the PMD are virtually totally elirninated by the DMUX device.
  • OSNR penalization refers to an OOK system in a back-to-back configuration for a 10 "12 Bit Error Rate (BER).
  • BER Bit Error Rate
  • FIG. 7 A quantitative estimate of the performance of the system is shown in Figure 7 showing the outage probability as a function of the mean Differential Group Delay (DGD) of the connection that is a characterizing parameter of the statistical behaviour of a fibre in PMD terms.
  • DGD Differential Group Delay
  • the PolMUX channel obtained in accordance with the present invention has decidedly better performance and shows that the device of the present invention is actually capable of demultiplexing the two channels and perfo ⁇ ning a compensation of the PMD even for orders higher than the first.
  • the proposed system can operate with mean DGD up to 0.42T b , keeping the OP below 10 "6 .
  • the DMUX device parameters are updated dynamically in such a manner as to follow the temporal variations of the transmission channel which are translated into changes in the fibre transfer 1 matrix.
  • a feedback signal which is a good indicator of the quality of the signals received, i.e. the corresponding error rate, is used to control the parameters.
  • the feedback signal is advantageously an estimate of the overall Mean Square Error (MSE) on the two signals received sj, s 2 (the sum or, equivalently, the mean square value of the MSE of each of the two signals). This is determined by the processing block 21.
  • the DMUX device can advantageously be controlled in response to other feedback signals, such as for example the sum (or mean value) of the openings of the eye diagrams (eye opening).
  • the Mean Square Error is the expected value of the square of the difference between the value of the received signal s ⁇ (tj), at the generic instant of sampling t,-, and the corresponding transmitted symbol an'.
  • control block 20 a minimization algorithm based on the gradient method is advantageously implemented.
  • the Q parameters of the DMUX 17 are continually updated on the basis of this algorithm such as to minimize the feedback signal.
  • various algorithms can be used as will be readily imaginable to those skilled in the art, such as the algorithm of Newton and its derivatives, the algorithm of Levenberg-Marquardt or the random algorithms like 'simulated annealing'.
  • the two signals ai and a 2 are described as being mutually independent, that is they correspond to two distinct communications data streams, they can also be taken as decoding signals (for example multilevel) of a signal to be transmitted. It will be clear to those skilled in the art that in this case the two received signals ⁇ j and ⁇ can be used to obtain reverse decoding and recover the transmitted signal.
  • Equations (10) and (11) are indicative of the fact that the present invention can be used for various alternative modulation formats. Notwithstanding the modulation format used, the vectors defined in (7) can be respectively considered as the Jones representation of the field at the fibre input, the Jones representation of the corresponding field at the fibre output, and the Jones representation of the field at the output of the DMUX assuming that the signals on the two outputs of the DMUX are the two orthogonal polarizations of the same field.
  • the feedback signal is an estimate of the MSE mediated on all the channels 10 associated with the modulation. For example, considering a PolSK eight-level modulation, three different channels are associated with the three Stokes parameters of the optical signal. The MSE is then estimated for each of the three channels received and mediated on them.
  • the-DMUX device can comprise polarization controllers and polarization mamt ⁇ ini-rig fibres such as described in the above-mentioned European Patent Application number EP1456980 followed by another polarization controller and 20 polarization divider as will readily imaginable to those skilled in the art in the light of the explanations given herein.
  • a particular feedback signal the mean square error MSE, and a particular minimization algorithm, the gradient algorithm.
  • Other feedback signal capable of monitoring the quality of the two channels received as well as another minimization or maximization algorithm can be used.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Optical Communication System (AREA)

Abstract

L'invention concerne un système de transmission multiplex de polarisation (10) dans lequel deux signaux optiques (z1, z2) sont transmis sur la même fibre optique (15) à la même longueur d'onde, mais avec des polarisations orthogonales. Le système se caractérise par le fait qu'il comprend un dispositif de réception (10) pouvant filtrer les deux composantes de polarisation orthogonale du signal reçu en fonction d'une matrice de transfert appropriée contrôlée de façon dynamique sur la base des signaux de sortie. Le système permet d'approcher la matrice de transfert inverse de la fibre dans la zone du spectre occupée par le signal, de compenser la dispersion de polarisation de mode (PMD) et la rotation de polarisation introduite par la fibre, d'éliminer les effets de distorsion et d'interférence mutuelle pour les deux signaux et d'obtenir ainsi une sortie démultiplexée correspondant aux deux signaux transmis.
PCT/EP2005/051061 2004-03-09 2005-03-09 Systeme, procede et dispositif de compensation de dispersion de polarisation de mode et de demultiplexage de signaux multiplexes de polarisation WO2005086391A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US10/598,718 US7873282B2 (en) 2004-03-09 2005-03-09 System, method and apparatus for polarization mode dispension compensation and demultiplexing polarization multiplexed signals
EP05716976A EP1723737A1 (fr) 2004-03-09 2005-03-09 Systeme, procede et dispositif de compensation de dispersion de polarisation de mode et de demultiplexage de signaux multiplexes de polarisation
JP2007502345A JP2007528175A (ja) 2004-03-09 2005-03-09 偏波モード分散補償と偏波多重信号の分波のためのシステム、方法及び装置

Applications Claiming Priority (2)

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IT000446A ITMI20040446A1 (it) 2004-03-09 2004-03-09 Sistema metodo e apparato per la compensazione della pmd e contemporanea demultiplazione di coppie di segnali multiplati ion polarizzazione
ITMI2004A000446 2004-03-09

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EP (1) EP1723737A1 (fr)
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EP2383910A1 (fr) * 2010-04-30 2011-11-02 Fujitsu Limited Système de transmission optique, transmetteur, récepteur et procédé
CN103107853A (zh) * 2013-01-23 2013-05-15 河北四方通信设备有限公司 基于数字相干接收机的光通信系统及输出信号的处理方法

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CN101630978A (zh) * 2008-07-14 2010-01-20 北京大学 实现偏振模色散补偿的方法、装置及系统
CN101729149A (zh) * 2008-10-22 2010-06-09 华为技术有限公司 一种光解偏振复用光载波的方法、装置和系统
JP5387113B2 (ja) * 2009-04-20 2014-01-15 日本電気株式会社 光受信装置
CN101645739B (zh) * 2009-09-14 2013-11-06 武汉邮电科学研究院 偏振解复用装置、偏振复用光通信系统及实现方法
JP5527418B2 (ja) * 2009-10-30 2014-06-18 富士通株式会社 偏波散乱補償装置および偏波散乱補償方法
JP5585115B2 (ja) 2010-02-18 2014-09-10 日本電気株式会社 光受信機、光通信システム及び光通信システムの等化方法
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CN103109481B (zh) * 2011-07-25 2015-11-25 华为技术有限公司 非线性的补偿方法、装置及信号接收系统
US8909045B2 (en) * 2011-12-07 2014-12-09 Cisco Technology, Inc. Multiprotocol transport using polarization division multiplexing
GB201603305D0 (en) * 2016-02-25 2016-04-13 Isis Innovation Method of designing an interferometer
GB201605120D0 (en) * 2016-03-24 2016-05-11 Univ Aston System and method for the transmission of optic signals
CN106053938B (zh) * 2016-06-18 2018-09-28 西安电子科技大学 利用双偏振调制器实现瞬时微波频率测量的装置及方法
JP7101569B2 (ja) * 2018-08-31 2022-07-15 住友電気工業株式会社 光受信装置の組立方法
CN110266385A (zh) * 2019-07-05 2019-09-20 南方科技大学 一种可见光通信方法及系统
CN111711490B (zh) * 2020-05-27 2023-05-02 西南交通大学 一种Stokes空间的快速偏振追踪与解复用方法
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CN115499057B (zh) * 2022-09-21 2024-09-20 聊城大学 一种基于密度矩阵理论的模式色散的监测补偿方法
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US7873286B2 (en) 2007-10-19 2011-01-18 Ciena Corporation Optical receiver systems and methods for polarization demultiplexing, PMD compensation, and DXPSK demodulation
US8005375B2 (en) 2007-10-19 2011-08-23 Ciena Corporation Optical receiver systems and methods for polarization demultiplexing, PMD compensation, and DXPSK demodulation
EP2383910A1 (fr) * 2010-04-30 2011-11-02 Fujitsu Limited Système de transmission optique, transmetteur, récepteur et procédé
US8737840B2 (en) 2010-04-30 2014-05-27 Fujitsu Limited Optical transmission system, transmitter, receiver and method
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CN103107853B (zh) * 2013-01-23 2015-07-08 河北四方通信设备有限公司 基于数字相干接收机的光通信系统及输出信号的处理方法

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US7873282B2 (en) 2011-01-18
ITMI20040446A1 (it) 2004-06-09
CN1977477A (zh) 2007-06-06
JP2007528175A (ja) 2007-10-04
US20080159741A1 (en) 2008-07-03
EP1723737A1 (fr) 2006-11-22

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